Template for use in manufacturing an implant for spinal or other orthopaedic fixation and method of manufacturing such an implant

ABSTRACT

A template for use in producing an implant for use in spinal or other orthopaedic fixation is provided,
         wherein the template ( 10, 60 ) is configured to change its configuration between a first configuration in which the template ( 10, 60 ) is capable of bending in response to a force and is capable of retaining a bent shape and a second configuration in which the template ( 10, 60 ) assumes a memorized shape in response to directing the temperature to a recovery level,   wherein the recovery level of the temperature is above body temperature. A spinal or orthopaedic implant ( 20 ) is formed by duplicating the bent shape of the template

The invention relates to a template for use in manufacturing an implantfor spinal or other orthopaedic fixation and to a method ofmanufacturing such an implant. The template is capable of bending inresponse to a force and is capable of retaining a bent shape which isused to model the implant with a shape corresponding to the shape of thetemplate.

It is known in the medical art to use spinal rod templates for modellingthe shape of a permanent rod that is used for stabilizing the spine bymeans of a screw-rod system. The necessary shape and length of thespinal rod which is to be implanted into a patient is determined on thebasis of the rod template which is a rod that is initially bent andmeasured to conform to the effected part of the patient's spine. The rodtemplate is then utilized for the configuring of the permanent rod whichis to be implanted into the patient and secured to a portion of thelength of the spine. Such templates are, for example, known from U.S.Pat. No. 6,221,077 B1.

The rod templates are bent manually or with a tool in the operating room(OR). To permit bending in the OR, rod templates known in the art can bemade of an aluminium alloy, for example AlMg—Si, having a relatively lowstrength. After use in the manufacture of the permanent rod implants,the rod templates are bent back and sterilized for using them a secondtime. This procedures may be repeated several times. However, the usedrod templates may still have a remaining curvature. In addition, theremay be a risk of breaking when the rod templates are bent and bent backseveral times.

US 2010/0063548 A1 describes a spinal correction template having a firstconfiguration which substantially corresponds to an uncorrected shape ofa spine. The spinal correction template can be activated such that thetemplate achieves a second configuration to cause the spine to assume anorientation substantially corresponding to the second configuration ofthe spinal correction template. In one embodiment, the spinal correctiontemplate can be formed of a shape-memory alloy such as Nitinol. The stepof activating occurs at a temperature in the range of about 28° C. toabout 37° C. Hence, the template can have an austenite finishtemperature (A_(f)) that is below body temperature (about 37° C.). Aspinal correction method using the template further includes attaching aprimary spinal rod to at least a portion of a spine after the spineachieves a corrected orientation, and removing the spinal correctiontemplate. A secondary spinal rod may be inserted in place of the spinalcorrection template. In some embodiments, the spinal correction templatecan remain in the patient's body.

It is the object of the invention to provide a template for use inmanufacturing an implant for spinal or other orthopaedic fixation thatcan be bent in the OR at about room temperature and that is reusableseveral times. Further, a method of manufacturing such a template and amethod of manufacturing an implant with such a template shall beprovided.

The object is solved by a template according to claim 1, a method formanufacturing the template according to claim 14 and a method forproducing an implant using the template according to claim 15. Furtherdevelopments are given in the dependent claims.

The template is configured to change its configuration between a firstconfiguration, in which template is capable of bending in response to aforce and is capable for retaining a bent shape, and a secondconfiguration in which the template assumes a memorized shape inresponse to directing the temperature to a recovery level, and whereinthe recovery level of the temperature is above body temperature. By bodytemperature, a temperature of around 37° C. is meant. Hence, thetemplate is in the first configuration during its intended use ofbending it in the OR outside or inside a patient's body.

With such a template, the curvature of the section of the spine that hasto be corrected or the shape of a bone plate which is intended to bridgebone parts or bones to be immobilized can be reproduced by bending orcontouring the template with low force in the OR, either manually orusing a tool. The bending or contouring the implant can be performedbefore or while surgery takes place.

Afterwards the implant can be manufactured by duplicating the shape ofthe template using another material for the implant and applying higherforces, usually with a tool.

With the template, difficult shapes can be easily reproduced and animproved anatomical contour can be obtained.

The memorized shape of the template, such as a straight or even shape,can be easily achieved by heating the template to a temperature abovethe recovery level so that the template automatically assumes thememorized shape. A step of bending back is no longer necessary. Afterrecovery of the memorized shape the template may be re-used for anotherprocedure. The transformation from the first configuration to the secondconfiguration and vice-versa is reversible. Therefore, the template canbe re-used a great, even an infinite number of times. An active coolingstep is not needed to achieve the first configuration. If the templateis not kept at a temperature above the recovery level, the temperatureof the template automatically decreases so that the template assumes thefirst configuration in which it is deformable.

Further, it is possible to revise the formed shape of the templatethrough mild heating to a temperature below the recovery level.

The template may be, for example, a spinal rod or a bone plate. The rodtemplate may be used for producing a spinal rod for correcting adeformity or misalignment in the spinal column caused by disorder suchas, for example, scoliosis or caused by injuries. Templates forproducing bone plates with a bent shape may be used, for example, in thecase of fractures of the hand or the shoulder.

In one embodiment, the template is made of a nickel-titanium (NiTi)alloy with an austenite finish temperature (A_(f)) which is above bodytemperature, in particular above 45° C., preferably above 50° C., morepreferably above 60 C and most preferably about 70° C. to about 80° C.Hence, the second configuration which is the memorized shape, can beeasily achieved by sterilizing the template with the usual procedure ofsterilizing medical instruments, such as vapour sterilization or byimmersing it in hot water. Thereby, the recovery level of the templateto achieve the memorized shape is easily achieved. The NiTi alloy isbiocompatible, therefore, the template is usable inside and outside thehuman body.

In one embodiment, the NiTi alloy comprises around 49.0 to 52.0 at.-%(atomic percent) nickel, more preferably 49.5-50.0 at. % nickel. Theremainder is titanium. Hence, the alloy is a martensitic shape memoryalloy that has a martensite finish temperature (M_(f)) that is aboveroom temperature. By room temperature a temperature of around 23° C.±3°C. is meant.

The strength, in particular the bending stiffness of the template madeof this material is less than that of conventional AlMgSi templates.Hence, the template can be bent with less force.

The template can be manufactured in a simple manner includingconventional steps of hot drawing and annealing. Thereafter, thetemplate may be cut to size and may be laser marked and finally cleaned.

During manufacturing, the template may obtain an oxide layer on thesurface, in particular during a step of annealing. The oxide layer has acolour that differs from the colour of the surfaces of the implants.Therefore, the template can be easily distinguished from the implants.The oxide layer also allows laser marking and imprinting other markings,such as length scales etc.

In the case of the NiTi template, the detection under X-rays is improveddue to the higher density compared to the conventional AlMgSi templates.

Further features and advantages of the invention will become apparentfrom the description of embodiments by means of the accompanyingdrawings. In the drawings:

FIG. 1 shows a schematic view of a first embodiment of the template in asecond configuration.

FIG. 2 shows a schematic view of the first embodiment of the template ina first configuration.

FIG. 3 shows a schematic view of the template of the first embodimentadapted to the desired curvature of the portion of the spinal column tobe treated and an implant produced on the basis of the template.

FIG. 4 shows a schematic perspective view of a second embodiment of thetemplate in a first configuration.

Referring to FIGS. 1 and 2, a first embodiment of the template realizedby a rod 10. The rod 10 extends between opposite ends 10 a, 10 b. It mayhave a cylindrical shape throughout its length and may have the samecross-sectional diameter through its entire length. However, it shall beunderstood that the rod 10 may have any cross-sectional shape deviatingfrom a cylindrical shape which can be the same or can vary along thelength of the rod. The rod 10 can be solid, i.e. without cavities insideor at the surface.

In a second configuration, shown in FIG. 1, the rod 10 assumes amemorized shape. In the embodiment, the memorized shape is a straightshape. However, any other pre-configured memorized shape can becontemplated, such as a shape with a slight curvature between the ends10 a, 10 b. The rod 10 is configured to assume the second configurationin response to directing the temperature acting onto the rod 10 to arecovery level. As long as a temperature acting onto the rod 10 is abovethe recovery level, the rod 10 is configured to maintain the memorizedshape.

FIG. 2 shows the rod 10 in a first configuration in which it is capableof bending in response to a force, such as a force exerted by the hands50 of a user. In the first configuration, the rod 10 is capable ofretaining a bent shape when the bending force is no longer applied. Therod 10 is in this first configuration at a temperature level of lessthan the recovery level, for example at body temperature or less, suchas at room temperature.

The rod 10 includes a shape memory material that is characterized byhaving two distinct configurations and the ability to restore itself,for example by heating it to a temperature above the recovery level, toa memorized shape that has been pre-configured.

More specifically, the material of the rod 10 is a shape memory alloyand still more specifically a nickel-titanium alloy (NiTi alloy)exhibiting the shape memory effect. In the first configuration, thematerial is in the martensitic metallurgical state where the rod 10 isflexible and deformable and can be caused to assume any of a variety ofshapes. Hence, the rod 10 can be bent by exerting a low force, forexample manually, onto the rod 10 to cause the rod 10 to assume a bentshape. By directing the temperature above the recovery level, i.e. byheating the rod 10 to a temperature above the recovery level, thematerial assumes the austenitic metallurgical state wherein the rod 10is rigid and assumes the memorized shape. The temperature at which thematerial begins to transform into the austenitic metallurgical state isthe austenite start temperature (A_(s)) and the temperature at which thematerial has fully transformed into the austenitic metallurgical stateis the austenite finish temperature (A_(f)). In the case of the NiTialloy, the recovery level can be defined as the austenite finishtemperature (A_(f)).

When the temperature of the rod 10 falls below the temperature of therecovery level, the material reaches the martensite start transformationtemperature M_(s) at which temperature the austenitic metallurgicalstructure begins to transform into the martensitic metallurgicalstructure. At the martensite finish temperature M_(f) the alloy iscompletely converted into the martensitic state. When the rod isreheated, the transformation back to the austenitic structure begins atthe austenite start temperature A_(s) and is completed at the austenitefinish temperature A_(f). The transition temperatures A_(f), A_(s),M_(f) and M_(s) are determined with a method according to ASTM F2082-06that is a standard test method for determination of the transformationtemperatures of nickel-titanium shape memory alloys by bend and freerecovery.

In the preferred embodiment, the A_(f) temperature is selected to beabove body temperature, for example above 45° C., preferably above 50°C., more preferably above 60° C. and most preferably between about 70°C. to about 80° C. An upper limit of the A_(f) temperature may be about90° C. to about 100° C. The martensite finish temperature M_(f) ispreferably above room temperature. It depends on the A_(f) temperatureof the alloy. For example, a template having an A_(f) temperature ofabout 80° C. may have an A_(s) temperature of about 60° C., a M_(s)temperature of about 50° C. and a M_(f) temperature of about 40° C.

A particular example for shape memory alloy of the rod 10 according tothe first embodiment is a so-called martensitic nickel titanium alloywith a nickel content that is less than that of nickel titanium alloyshaving superelastic properties, i.e. preferably less than about 50.6 to51.0 at.-% nickel according to the standard ASTM F 2063. For example,the nickel content of the alloy according to an embodiment 49.0 to about52.0 at. %—nickel, preferably about 49.5 to about 50.0 at.-% nickel. Theremainder is titanium. Small portions of impurities may be present aslisted in ASTM F 2063. An example of such an alloy is SM 495. Thismaterial can be deformed at room temperature and is transformed back tothe austenitic metallurgical state at a temperature A_(f) higher thanbody temperature.

The rod 10 may have on its surface an oxide layer that is obtainedthrough annealing during a step of manufacturing the rod 10. The oxidelayer may have a color that is darker than conventional oxide layers ofpermanent implants. This results from the fact that the oxide layerobtained through annealing is thicker than conventional oxide layers onimplants that may be obtained by anodic oxidation. The oxide layer mayrepresent a marking to distinguish the rod by its color from implants.

On the surface of the rod 10 markings (not shown) may be provided thatare obtainable by laser marking. Such markings can include CE marking,LOT-number marking and/or other markings. For example, the rod 10 mayhave incremental distance markings.

A flexural strength of the rod 10 in the first configuration is, forexample, around 100-150 N/mm². The rod may have a diameter correspondingto usual diameters of spinal correction rods, for example, a diameter of3.5 mm, 4.5 mm, 5.5 mm etc. The density of the material of the rod maybe considerably higher than that of convention AlMgSi rods, for example,around 6 g/cm³ or higher. This causes improved detection through X-rays.

A method of manufacturing the template rod 10 includes steps of forminga pre-configured shape, memorizing the pre-configured shape such thatthe template has the pre-configured memorized shape in the austeniticmetallurgical state. The manufacturing steps include hot drawing andannealing. Typical conditions for annealing are annealing at around 350°C. to around 800° C. for around 5 minutes to around 60 minutes. Suitableconditions may be selected dependent on the specific composition of thealloy. By the annealing, the oxide layer is obtained. The method mayfurther include steps of cutting to size and/or of laser marking and/orof cleaning the template.

Turning now to FIG. 3, use of the template is shown schematically. Therod 10 is bent in the OR along the actual curvature or the desiredcurvature of the portion of the spinal column 100 including a number ofvertebrae 200. In the OR, there is normally room temperature so that therod 10 is in the martensitic metallurgical state. It can be easily bentmanually or with a device. Alternatively, the rod 10 is inserted intobone anchors (not shown) implanted in the vertebrae to be stabilized. Inthis case, the bending takes place in the body of the patient. As therecovery level of the temperature is above body temperature (about 37°C.), the rod 10 is still in the martensitic metallurgical state. Afterthe desired curvature is achieved, the rod 10 forms the template for apermanent spinal rod 20 that is bent to have a duplicate shape of therod 10. Bending of the rod 20 may be performed with a device. Thepermanent spinal rod 20 is then inserted into the bone anchors (notshown) to stabilize the portion of the spine to be treated.

Turning now to FIG. 4, a second embodiment of the template is shownwhich is in the form of a bone plate 60. The bone plate 60 as shown hasan elongate shape, i.e. its greatest length is greater than the greatestwidth. The thickness of the bone plate 60 is such that the bone plate 60can be bent in the first configuration as depicted in FIG. 4 by exertinga force with the hands 50. It is not necessary that the thickness of thebone plate 60 is identical to the thickness of a permanent bone plateimplant to be manufactured using the template bone plate 60. The boneplate 60 is made of the same material as the rod 10 according to thefirst embodiment. Hence, the properties of the bone plate 60 with regardto the first configuration and the second configuration are identical.In the second configuration, the bone plate 60 is in the memorizedshape, which may be a straight shape, but can also be a slightly bentshape. The contour of the bone plate 60 can be any contour, such asrectangular, irregular, square, oval etc.

The method of manufacturing the bone plate 60 and the method ofproducing a permanent bone plate implant are the same as described forthe first embodiment.

Further modifications of the above described embodiments may becontemplated. For example, instead of spinal rods or bone plates, anyother orthopaedic components or implants may be manufactured using acorrespondingly shaped template, such as bone nails or pegs or hooks.

Instead of a nickel titanium alloy, other shape memory alloys or shapememory polymers (SMPs) can be used. Such shape memory polymers mayinclude linear block copolymers, for example shape memory polyurethane,thermoplastic polymers, for example polynorbornene, or chemicallycross-linked SMPs. The recovery level is then defined as the temperatureat which the material begins to transform into the first configurationto reach its memorized shape.

The memorized shape can be any shape. Hence, bending the template andthe resulting bent shape of the template in the first configurationincludes generating a deviation form the memorized shape.

1. A template for use in producing an implant for use in spinal or otherorthopaedic fixation, wherein the template is configured to change itsconfiguration between a first configuration in which the template iscapable of bending in response to a force and is capable of retaining abent shape and a second configuration in which the template assumes amemorized shape in response to directing the temperature to a recoverylevel, wherein the recovery level of the temperature is above bodytemperature.
 2. The template of claim 1, wherein the shape of thetemplate is a rod or a plate.
 3. The template of claim 1, wherein thetemplate comprises a shape memory material.
 4. The template of claim 1,wherein the template is made of a nickel-titanium shape memory alloy. 5.The template of claim 4, wherein the template is in the firstconfiguration in the martensitic state.
 6. The template of claim 4,wherein the recovery level of the temperature is the austenite finishtemperature which is above 45° C., preferably above 50° C., morepreferably above 60° C. and most preferably between about 70° C. andabout 80° C.
 7. The template of claim 4, wherein the alloy comprisesabout 49.0 to 52.0 at. % nickel, preferably about 49.5 to 50.0 at. %nickel.
 8. The template of claim 4, wherein the alloy comprises about48.0 to 51.0 at. % titanium, preferably about 50.0 to 50.5 at. %titanium.
 9. The template of claim 1, wherein the template is in thefirst configuration during room temperature.
 10. The template of claim1, wherein the template is capable to assume its second configurationduring a sterilization process, for example vapour sterilization, asused for medical instruments or by immersing it into a hot fluid, suchas hot water.
 11. The template of claim 1, wherein the template iscapable to assume the first configuration upon directing the temperaturebelow the recovery level and wherein the transformation from the firstconfiguration to the second configuration and vice versa can be made atleast two, preferably a plurality of times.
 12. The template of claim 1,wherein the template comprises a surface with a colour different fromthe colour of the surface of the implant to be produced, preferably asurface formed by an oxide layer.
 13. The template of claim 1, whereinthe memorized shape of the template is a straight shape.
 14. A method ofmanufacturing a template according to claim 1, the method comprising thesteps of forming a shape of the template by hot drawing, annealing thetemplate.
 15. A method of manufacturing an implant for spinal or otherorthopaedic surgery, the method comprising the steps using a templateaccording to claim 1 in the first configuration after it has been bent;forming the implant from a semi-finished implant by bending thesemi-finished implant corresponding to the bent shape of the template.